No abstract

We tested a recent Habitat Suitability Index (HSI) model proposed for the Swainson's warbler (Limnothlypus swainsonii; a species of conservation concern in the southeastern United States) using data on habitat, bird occupancy, and abundance collected at White River National Wildlife Refuge, Saint Francis National Forest, and Big Island in Arkansas between 2005 and 2010. The Swainson's warbler HSI includes a combination of 6 variables: landform, landcover, successional age class, forest patch size, proportion forest in a 1-km radius, and small-stem density (<2.5 cm diam breast ht; these variables are combined to produce scores ranging 0-1, representing unsuitable to optimal habitat. Mean HSI scores were significantly lower (x ¼ 0.65, n ¼ 99) for sites occupied by Swainson's warblers compared with unoccupied locations (x ¼ 0.78, n ¼ 177) at White River National Wildlife Refuge and Big Island, contrary to our expectation for a useful model. We also found that Swainson's warbler abundances were not correlated with HSI scores both at Saint Francis National Forest and at White River National Wildlife Refuge. Our tests of the current Swainson's warbler HSI model demonstrate that it was not an effective predictor of Swainson's warbler occupancy and was not a reliable indicator of warbler habitat at the scale of our study areas. We propose a new suitability function called proportion elevation that takes relative elevation into account at potential sample locations that may improve the model. Specifically, this function should index the likelihood a site is infrequently flooded and should support the development of a thick understory, a habitat feature that has been demonstrated to be important to Swainson's warblers. Ó

Large-scale disturbances, by affecting habitat suitability, can influence bird populations and communities. Although we know that disturbances can lead to population decreases and shifts in community structure, our understanding of finer-scaled mechanisms leading to these patterns is limited. We focused on why some territories remain occupied by a species following a large-scale disturbance, while others are abandoned. The Swainson's Warbler (Limnothlypis swainsonii) is especially susceptible to flooding because of its preference for nesting in thick understory vegetation and foraging in leaf litter. In 2008, a major flood inundated a study site where we have studied Swainson's Warblers since 2004. In 2008 and 2009, we resurveyed 42 Swainson's Warbler territories that were occupied between 2005 and 2007 and examined changes in habitat structure and composition and prey abundance influencing territory abandonment. Occupancy declined between the preflood and postflood surveys. Territory abandonment was associated with decreases in leaf litter cover, increases in cover of green vegetation, and decreases in density of total understory stems and giant cane (Arundinaria gigantea) between the preflood and flood periods. Despite the partial recovery of habitat structure and prey abundance after the flood, Swainson's Warbler occupancy did not recover in subsequent years. Multiple habitat variables, including leaflitter cover, density of woody stems, understory density, and prey abundance have been identified as important for Swainson's Warblers, and these results suggest that leaf litter may be espeeially important in influencing habitatselection decisions following flood disturbance. Mecanismos de Abandono del Territorio Inducido por Inundaciones en un Ave que Forrajea de Modo Obligado en el SueloResumen. Los disturbios de gran escala, al afectar la aptitud del habitat, pueden influenciar a las poblaciones y comunidades de aves. Aunque sabemos que los disturbios pueden llevar a disminuciones poblacionales y cambios en la estructura comunitaria, nuestro entendimiento de los mecanismos de sintonia fina que llevan a estos patrones es limitado. Nos enfocamos en entender por qué una especie continúa ocupando algunos territorios luego de un disturbio de gran escala, pero abandona otros. Limnothlypis swainsonii es una especie particularmente susceptible a las inundaciones debido a sus preferencias por anidar en la vegetación densa del sotobosque y por forrajear en la hojarasca. En 2008, una gran creciente inundó un sitio de estudio donde hablamos estudiado a L, swainsonii desde 2004. En 2008 y 2009, volvimos a muestrear los territorios de 42 individuos de L. swainsonii que estuvieron ocupados entre 2005 y 2007 y examinamos los cambios en la estructura y composición del habitat y la influencia de la abundancia de presas en el abandono del territorio. La ocupación disminuyó entre los muestreo previos y posteriores a la inundación. El abandono del territorio estuvo asociado con la disminución de la cobertura de la hojarasca, el au...